The present invention is related to mass flow sensors, in general, and more particularly, to a sensor and method of non-intrusively measuring mass flow of a medium flowing through a tube.
Intrusive mass flow sensors of the thermal type generally involve disposing a heated probe through a wall of the tube and into the flow stream of the medium. The mass flow is measured by virtue of its relation to the convection heat transfer coefficient that is related to the thermal gradient measured at two points along the length of the probe, preferably at the base and tip of the probe. One example of such an intrusive mass flow sensor is provided in the U.S. Pat. No. 6,487,904, issued Dec. 3, 2002, entitled “Method and Sensor For Mass Flow Measurement Using Probe Heat Conduction” and assigned to the same assignee as the instant application.
Some applications can not tolerate an intrusive sensor, i.e. a sensor which has at least one probe penetrating the wall of the flow tube. In addition, in those applications in which the power source may be limited, power consumption of a sensor probe in the flow stream may exceed the capacity of the power source. Moreover, disposing an intrusive probe into the flow stream will produce a pressure drop that may undesirably limit the flow of the medium through the tube.
Accordingly, what is desired is a non-intrusive alternative mass flow sensor and method that produces no pressure drop in the medium flow and functions with a low power consumption. The present invention offers such an alternative non-intrusive mass flow sensor and method.